This invention relates to luminous dot sighting instruments and more particularly to such instruments used in connection with a telescope on a firearm as an aid to sighting the firearm on a target.
Optical sighting instruments having a sighting tube that often contains a telescope have used cross hairs to define the optical center of the instrument, and the user, such as a firearm marksman, places the cross hairs on the target in the view to aim the firearm. Clearly, the cross hairs are illuminated by light from the view. At twilight, in haze or fog and at other times when visibility is low, the cross hairs are difficult to see, and at night they cannot be seen at all. One solution to this problem has been the luminous dot sighting instrument.
A luminous dot sighting instrument is used to view a target and may be attached to a rifle or other firearm to sight the rifle on the target. The luminous dot is generated inside the instrument and is superimposed on the view of the target and serves the purpose of cross hairs. It does not depend on light from the view and can be made as bright as desired by the user. Often the luminous dot sighting instrument is used in conjunction with a telescope and along with the telescope is attached to a rifle to aid the marksman in pointing the rifle to hit the target viewed through the instrument and the telescope.
In a reflex type luminous dot sighting instrument, light is projected from a luminous source, such as a light emitting diode (LED) contained in the instrument, onto an inclined lens having a mirror coating so that light from the view passing through the lens is joined by light from the diode that reflects from the mirror coating. The marksman sees the target view with the luminous dot at the center and points the rifle to place the dot on the target in the view and fires the rifle. With a properly mounted and adjusted sighting instrument the marksman can quickly view the target area, put the dot on the target and fire the rifle with great accuracy.
Heretofore, a number of reflex type luminous dot sighting instruments, some with telescopes and some without, have been used with adjustments for range and windage to be made by the firearm marksman. The adjustments for range and windage are adjustments in elevation angle and azimuth angle, respectively, of the instrument with respect to the firearm and are set by the marksman using his estimates of range and windage. In all of these, the target view and the luminous dot are combined by the inclined lens with a mirror coating and light from the target view passes through the inclined lens while light from the LED that forms the luminous dot reflects from the lens mirror coating. The light for the luminous dot is preferably from a point source and is focused by the lens mirror on the same image plane as the target view so that the marksman sees the target view and the luminous dot all in focus at the same plane with the luminous dot precisely at the center of the target view. Often an LED emitting red light is used and it is enclosed by an aperture that directs the red light as a narrow angular cone to the center of the inclined lens. Thus, the luminous dot appears to the marksman the same size, shape and color for all target views, at the center of the target view, whether the target is far or near (long or short range) and whether there is any adjustment for windage, left or right.